The separation of air into its major components by cryogenic rectification is a well established commercial process. Nitrogen is produced at very high purity using this process wherein the components of air are separated based on their relative volatilities. Of the major components of air, nitrogen is the more volatile and thus lower boiling impurities such as helium, hydrogen and neon concentrate in the nitrogen product. The concentration of these lower boiling impurities in the nitrogen product from a cryogenic air separation plant generally does not exceed 100 ppm and thus is not a problem for most uses of the nitrogen. However some nitrogen applications, such as in the electronics industry, require nitrogen of ultra high purity wherein the concentration of lower boiling impurities is much lower than is possible with conventional air separation.
Accordingly it is an object of this invention to provide a cryogenic rectification air separation process which can produce nitrogen of ultra high purity wherein the concentration of lower boiling impurities is much lower than is possible with conventional air separation.